The invention relates to a drying cylinder for a paper making machine, or the like, and more particularly to means for attaining uniform drying across the width of the web being dried.
The cylinder includes a casing which is grooved on its inner surface and includes a siphoning arrangement provided inside the cylinder for extracting condensate from the grooves in the casing.
The siphoning arrangement generally includes a number of elements, now described. At the points at which the condensation gathers, namely, at the peripheral grooves in the cylinder casing, small suction pipes are provided. These project into the peripheral grooves. Axially extending condensate collectors located inside the casing are connected to the many small suction pipes for receiving the condensate therefrom. The condensate collectors are, in turn, connected to siphon pipes which generally extend substantially radially of the casing. The siphon pipes, in turn, lead to an axially extending main condensate drainage line.
Despite numerous improvements in paper making machines, and in particular in the drying sections of the paper making machines, there has been a continuous problem that, viewed across its width, the paper web is unevenly damp (or unevenly dry). Particularly with large drying cylinders for producing lightweight crepe paper, the evenness of the drying over the whole length of the cylinder is decisive for the quality and quantity of the paper. Relatively small variations in the drying condition of the paper web produce very disadvantageous effects in its quality.
Improving the quality of paper produced in a paper making machine has been a prime concern of modern research in connection with paper making machines. The evenness of the drying profile of the paper web has been the subject of repeated research efforts. This research has been difficult since there are a number of sources of disturbance which cause a poor drying profile. The following possibilities should be noted. Moisture which is present at certain points in the paper web can be drawn in from the wet part. This may thus be attributed to faults in the head box of the paper making machine, for example, a bowed delivery lip, faults in the press section, faults in the wet felt web, blocked holes in a suction pressure roller, faults in the spraying pipes, etc. Furthermore, there may also be faulty operation of the hot air cowl. Cambering faults in a pressure roller may cause uneven drying. All these disturbance factors have been investigated and at least partially eliminated. Complete elimination of all drying irregularities has not been achieved up to the present time.